1. Field of the Invention
The present invention relates to auxiliary load support axle assemblies for vehicles such as transit mixers, and specifically to a variable load transfer axle assembly mounted forwardly from the rear drive wheels of such vehicles.
2. Description of the Prior Art
In the prior art numerous forms of auxiliary axles or load support dollies have been utilized in combination with vehicles to partially support the weight of the vehicle and its load. Government highway or bridge weight regulations often require a specific number of axles when a vehicle's weight exceeds a certain limit. To compensate for such regulations for vehicles whose weights vary greatly depending upon whether they are loaded or not, auxiliary trailing or "tag" axles have been utilized adjacent the rearward ends of such vehicles to provide a load-carrying additional axle. Examples of such tag axle devices (which can be selectively lowered into engagement with the ground to assist in supporting the vehicle's weight) are shown in the following U.S. Patents:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 3,112,100 Prichard 11/26/63 3,161,418 Brennan et. al 12/15/64 3,191,961 Brennan et. al 06/29/65 3,246,884 Prichard et. al 04/19/66 3,317,193 Buelow et. al 05/02/67 3,479,049 Duecy 11/18/69 3,610,653 Derrwaldt 10/05/71 3,685,853 Goldsmith 08/22/72 3,704,896 Buelow 12/05/72 3,912,293 Harbers 10/14/75 4,314,709 Silbernagel 02/09/82 ______________________________________
All of the above patents show tag axles wherein the additional axle is provided to the rear of the drive wheels of the vehicles. Another type of tag axle design which is mounted rearwardly of a vehicle's drive wheels is made by Granning Suspensions, Inc. of Livonia, Mich. On elongated non-articulated vehicles, such a rearward placement of an auxiliary axle causes problems related to the steering and control of the vehicle, especially during cornering or turning maneuvers. An alternative placement position for an auxiliary axle is between the forward steerable wheels and the drive wheels of the vehicle. In this position on the vehicle, none of the prior art auxiliary axles can be raised to an extremely high position (as shown, for example, in U.S. Pat. No. 4,314,709 and U.S. Pat. No. 3,246,884) because of the presence of the vehicle drive shaft extending rearwardly from the motor of the vehicle to the drive wheels. The support structures or frames of the tag axles of the prior art are typically center-mounted and of such configurations as to interfere with the vehicles drive shaft. The extent of lift of an auxiliary axle placed forwardly of the rearward drive wheels of a vehicle is thus limited by the vehicle's frame and its drive shaft. An additional limitation is that some states require that each supporting axle of a vehicle be a continuous member extending laterally across the vehicle, thus preventing the use of separate stub axles on each side of the vehicle.
To compensate for the drive shaft of the vehicle, auxiliary axle assemblies placed forwardly of the rearward drive wheels have been provided with one-piece lateral axles having drop center portions to prevent interference of the auxiliary axle with the vehicle's drive shaft when the auxiliary axle is raised. Such a design also premits the auxiliary axle to be raised higher off of the ground. Such ground clearance (between the wheels of the auxiliary axle and the ground) is necessary for those times when the vehicle reaches the crest of a hill or must tranverse a ditch or gully to reach a desired location. If not enough lift is achieved, the wheels of the auxiliary axle will engage the ground and interfere with the operation of the drive or steering wheels of the vehicle. Prior art auxiliary axles were unable to obtain a clearance of greater than 63/4 inches for the lowermost portion of the wheels on the auxiliary axle. In many instances, that is simply not sufficient clearance for the vehicle to operate effectively.